1. Technical Field
The invention relates to a comparator of a mono-pulse radar. Particularly, the invention relates to a comparator having a transverse electromagnetic (TEM) mode cavity power combiner and a signal generation method thereof.
2. Related Art
Radar (radio detection and ranging) is widely used in military equipment and used for terrain detection, and is also commonly used to detect locations of objects. A working principle of the radar is to emit electromagnetic energy to space, and receive electromagnetic waves reflected by an object in the space, so as to calculate a direction, a height and a speed of the object, and detect a shape of the object. Along with scientific progress in various fields and continuous development of radar technology, connotation and research content thereof are continuously developed, and a mono-pulse technique is widely applied in different fields. Compared to the conventional radar, the mono-pulse radar can obtain information of the object such as direction, height, distance, etc. through only one pulse signal. Moreover, since the mono-pulse radar has advantages of uneasy to be interfered, high resolution, accurate angle detection, etc., it becomes one of the mainstreams of the modern radar system.
Since the mono-pulse radar detects the position information of the object by analyzing a reflected signal received by each antenna, the mono-pulse radar includes a comparator capable of changing the received reflected signal into a related signal containing phase comparison or amplitude comparison. Further, the comparator of the mono-pulse radar generates combination/difference signals according to the reflected signals received by the antennas, and a backend circuit may use the combination/difference signals to determine a space angle of the object. The conventional comparator in the mono-pulse radar is generally composed of a 90 degree or 180 degree coupler, so that the conventional comparator only can operate in a narrower operating bandwidth. FIG. 1 is a structural schematic diagram of a conventional comparator of a mono-pulse radar. Referring to FIG. 1, the comparator 10 has an antenna array 110, a 90 degree phase shifter 120, a 90 degree phase shifter 130, a 90 degree coupler 140, a 90 degree coupler 150, a 90 degree coupler 160 and a 90 degree coupler 170, and the antenna array 110 has an antenna 111, an antenna 112, an antenna 113 and an antenna 114.
The antenna 111 outputs a received reflected signal SA to the 90 degree coupler 140, and the antenna 112 outputs a received reflected signal SB to the 90 degree phase shifter 120. The antenna 113 outputs a received reflected signal SC to the 90 degree phase shifter 130, and the antenna 114 outputs a received reflected signal SD to the 90 degree coupler 150. Based on the structure shown in FIG. 1, the comparator 10 may output four types of combination/difference signals, which are respectively a sum signal SS, a height difference signal EDS, an azimuth difference signal ADS and another signal OS. The sum signal SS is equal to
                    (                  SA          +          SB                )            +              (                  SC          +          SD                )              2    ,the height difference signal EDS is equal to
                    (                  SA          +          SC                )            -              (                  SB          +          SD                )              2    ,the azimuth difference signal ADS is equal to
                    (                  SC          +          SD                )            -              (                  SA          +          SB                )              2    ,and the signal OS is equal to
                    (                  SA          -          SB                )            -              (                  SC          -          SD                )              2    .Therefore, the backend circuit of the radar that is connected to the comparator 10 may obtain a position and a space angle of the object according to the sum signal SS, the height difference signal EDS and the azimuth difference signal ADS.
However, in the conventional comparator of FIG. 1, regardless of the 90 degree phase shifters or the 90 degree couplers, component design criteria and operating wavelength thereof are all highly correlated, which represents that the operating bandwidths of these components are limited. Namely, limitation of the operating bandwidth of the 90 degree phase shifter or the 90 degree coupler results in reduction of a range of an operating bandwidth of the comparator of the mono-pulse radar. Therefore, regarding the mono-pulse radar, it is important to design a better comparator that is more in line with the needs.